The patients presenting acute coronary syndrome with or without ST segment elevation form a heterogeneous population and thus the short and long-term risk of death or recurrent ischemic events can vary considerably. During ACS without ST elevation (unstable angina and non-ST elevation MI), the evaluation of risk is an essential step in the management of such patients, because it determines ulterior strategy. This evaluation is simple and reliable, and is principally based on three scores: the TIMI, the GRACE Score or the PURSUIT. Thanks to this stratification, high and medium-risk patients are able to benefit from early invasive management (stents and anti-GPIIb/IIIa) as recent studies have clearly shown. Even if immediate management of patients with non-ST elevation ACS does not take account of risk stratification, using such information in the medium and long-term does help determine the prognosis. Finally, the risk profile score, whatever the score used is today an essential tool, which helps qualify and especially compare patients included in international clinical studies.